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Biomedical subjects

G Stark

Publications and source records attributed to G Stark.

At least 127 records · Page 7Linked to original sources
PubMed1990

White fingers after excessive motorcycle driving: a case report.

An 18-year-old male presented with Raynaud's phenomenon which was found to be caused by occlusion of the proper palmar digital arteries on the right hand and obstruction of the superficial palmar arterial arch on the left hand. These lesions in the arteries of both hands resemble those found in patients with vibration-induced white fingers such as in mine or foundry workers. The only likely cause for the pathological vascular findings in our patient was an exposure to vibration due to excessive off-street motorcycle driving. Therapy with intraarterial prostaglandins resolved the ischemic syndrome but it promptly recurred when the patient resumed motor cycle driving. Therefore, we suggest that excessive cross country motor cycle driving may cause vibration-induced white fingers.

Adolescent↗
PubMed1989

The influence of elevated Mg2+ concentrations on cardiac electrophysiologic parameters.

This study was performed to evaluate the direct effects of magnesium ions on cardiac conduction velocities and on refractoriness using a modified Langendorff perfusion system and a special ECG recording and stimulation technique. An increase of the MG2+ concentration to 2.3 mM had no detectable effects. Higher concentrations of up to 4.6 mM decreased the spontaneous sinus rate and the conduction velocity through the AV node and the His bundle in a concentration-dependent manner. During stimulation with premature beats, in the presence of 4.6 mM of Mg2+, the effective and relative refractory periods (ERP, RRP) of sinoatrial, AV nodal, and His bundle conduction and the ERP of the ventricular myocardium were significantly prolonged, whereas the ERP of the atrial myocardium remained unaffected. The refractoriness of sinoatrial, AV nodal, and His bundle conduction, and of the ventricular myocardium, were also prolonged during pacing with a stepwise increased pacing rate. These observations suggest a marked rate-dependent inhibitory effect of magnesium on the refractoriness of the His-bundle conduction and of the ventricular myocardium, which might be an important factor in the antiarrhythmic effectiveness of magnesium in ventricular tachyarrhythmias.

Animals↗
PubMed1989

Assessment of the conduction of the cardiac impulse by a new epicardiac surface and stimulation technique (SST-ECG) in Langendorff perfused mammalian hearts.

The assessment of the effects on the conduction of the cardiac impulse and of refractoriness simultaneously from multiple cardiac structures is important to evaluate the mode of action of new compounds, as well as to investigate undesired cardiac side effects. The measurements of intracardiac electrical activities of special structures have required catheter methods or averaging techniques to produce clear deflections of low-level potential wave forms. We have developed an epicardial surface electrocardiogram (S-ECG) recording technique to detect continuously sinus node and His-bundle activities in spontaneously beating Langendorff perfused heart preparations. A bipolar surface stimulation technique electrocardiogram (ST-ECG) could be combined with this S-ECG method to assess the effect of pacing at maximal rate on the refractoriness of the sino-atrial, AV-nodal, and His-bundle conduction, as well as that of the atrial and ventricular myocardium. Epicardial surface electrodes were also used for vector analysis of the signals, which include those of the sinus node and His-bundle potentials, in addition to the usual atrial and ventricular loops. The present results demonstrate that this new epicardial surface ECG recording technique, combined with the described SST-ECG, provided a way to improve or replace more elaborate intracardiac techniques used in isolated hearts or in animal experiments.

Animals↗
PubMed1988

Tumor necrosis factor-alpha affects LTR-controlled oncogene expression in transformed mouse fibroblasts at the post-transcriptional level.

Potential mechanisms of TNF-alpha action on tumor cells have been investigated in a model of mouse fibroblasts transformed by distinct retroviral vectors carrying the v-mos, c-myc, and v-Ha-ras oncogene, respectively. Treatment of v-mos and c-myc transformed cells with murine rTNF-alpha in non-cytotoxic concentrations caused a strong inhibition of both proliferative capacity in monolayer culture and colony formation in soft agar. In contrast, v-Ha-ras transformed cells showed little sensitivity to TNF-alpha treatment. These changes in cell growth characteristics of v-mos and c-myc transformants was preceded by a selective reduction of oncogene-specific steady RNA levels, whereas no RNA down-regulation was observed for v-Ha-ras transformants. An unchanged transcriptional activity of the LTR-controlled v-mos and c-myc genes, but a decreased half-life of oncogene-specific mRNA suggests that TNF-alpha primarily affects stability of v-mos and c-myc RNA without influencing the activity of retroviral promoters. This is confirmed by an unchanged chloramphenicol acetyl transferase activity in TNF-treated LTR-chloramphenicol acetyl transferase transformants. Removal of TNF-alpha from cultures of reverted cells provoked a rapid retransformation, with full recovery of neoplastic growth characteristics 10 days after abrogation of TNF-alpha treatment. These data suggest that in cases of non-cytocidal action of TNF-alpha persistent suppression of tumor cell growth requires continuous TNF-alpha treatment.

Animals↗
PubMed1988

[Change in impulse formation and impulse transmission of the heart in relation to high magnesium concentration].

The effects of magnesium ions on the cardiac conduction velocity and on the refractory periods of the single parts of Langendorff perfused guinea pig hearts were studied using a high amplifying ECG recording and a special stimulation technique. Concentrations of 2.3 mM or 3.45 mM Mg++ had only little inhibitory effects on the cardiac conduction velocity and on the sinus node activity. The elevation of the magnesium ion concentration to 4.6 mM caused a reduction of the spontaneous sinus rate and a prolongation of the AV nodal and His bundle conduction time. During stimulation with stepwise increasing pacing rate, a marked prolongation of the refractoriness of the His bundle conduction and of the ventricular myocardium was detectable. This frequency dependent inhibitory influence on the His bundle and the ventricular myocardium could be an explanation for the antiarrhythmic efficacy of magnesium ions during ventricular tachyarrhythmias.

Animals↗
PubMed1988

[Prostaglandin E1 in decreased arterial perfusion].

Prostaglandin E 1 has been used for the past 15 years in decreased peripheral arterial perfusion with differing degrees of success. The exact mechanism of action has not been clarified so far. Vasodilatation, increased fibrinolytic activity and an improved cellular metabolism were observed in response to PGE 1 in animal experiments both in vivo and in vitro. In the clinical studies performed so far PGE 1 has been used in cases of decreased peripheral arterial perfusion after functional, inflammatory, degenerative or diabetic arteriopathy (stages IIb-IV). Reduction or alleviation of ischaemic rest pain, as well as a faster healing of tissue necrosis was reported after intaarterial administration, especially in non-controlled, but also in controlled studies. Intravenous administration of PGE 1 had a positive influence on clinical symptoms in non-placebo-randomized patients; in the controlled studies, however, the results were not significant. The greatest therapeutic success can be achieved using intermittent intraarterial administration in decreased peripheral arterial perfusion due to functional or inflammatory arteriopathies.

Alprostadil↗
PubMed1988

Extraction of an infected tusk in an adult African elephant.

An 18-year-old African elephant was determined to have a nonrepairable crack in its left tusk. Treatment included extraction of the tusk, using rotational and extractional forces, and administration of antibiotics, followed by 1 year of flushing the opened tusk cavity with warm tap water. Two years after surgery, the elephant was healthy, and the tusk cavity was 80% filled with normal tissue.

Animals↗
PubMed1988

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes. II. Phloretin and phloretin analogues.

Phloretin and structurally related neutral molecules adsorb to the interface of lipid membranes and modify the electric dipole potential of the membrane/water interface. The adsorption process has been studied using a laser-T-jump relaxation technique in combination with an analysis of nonactin mediated potassium transport (see part I, Awiszus and Stark 1988). Deviations from the Langmuir isotherm were observed for most of the substances. The discrepancies were most pronounced at large surface densities, whereas good agreement was found at low concentrations in many cases. The partition coefficient in the limit of low concentrations was compared with that of octanol/water bulk phases. No correlation was found. The individual values of the two partition coefficients differed by more than three orders of magnitude. The contribution, b, of a single adsorbed molecule to the dipole potential could not be predicted from the dipole moment, microL, of the molecule measured in the bulk phase. Different values of b were found at identical values of microL. The study shows the limitations of the use of bulk phase data to predict molecular properties in lipid membranes.

Electric Conductivity↗
PubMed1988

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes. I. 2,4-dichlorophenoxyacetic acid.

The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of beta HA = 4.7 x 10(-4) cm, a rate constant of desorption kHA greater than or equal to 100 s-1 and a maximum surface density ND = 7.7 x 10(13)/cm2 were found. The concentration at half saturation is KHA = 2.7 x 10(-4) M. Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maximum dipole potential of VDmax = -239 mV and a contribution of b = 3.1 x 10(-15) V cm2 per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K+ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1988

[Simultaneous radiochemotherapy of locally advanced stage T4 breast cancer].

The local efficacy of simultaneous radiochemotherapy was tested in 17 women with 18 carcinomas of the breast in stage T4 only. Treatment was conducted for a period of 6 months with 6 courses of drug therapy (A + E) coordinated simultaneously with 6 courses of radiotherapy. In 72% of the cases we found considerable (greater than 80%) or complete (100%) regression of the tumour as a result of this combined treatment. The median survival time is 35 months.

Aged↗